A radio access scheme and a radio network for cellular mobile communication (hereinafter, referred to as “Long-Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access: EUTRA”) have been examined in the 3rd Generation Partnership Project (3GPP). In the LTE, a base station apparatus (base station) is also referred to as Evolved Node B (eNodeB), and a terminal device (mobile station, mobile station apparatus, or terminal) is also referred to as user equipment (UE). The LTE is a cellular communication system in which a plurality of areas within the coverage of the base station apparatus is arranged in the form of cells. A single base station apparatus may manage a plurality of cells.
The LTE supports frequency-division duplexing (FDD) and time-division duplexing (TDD). The LTE that adopts the FDD system is also referred to as FD-LTE or LTE FDD. The TDD is a technology that enables full-duplex communication in at least two frequency bands by performing frequency-division multiplexing on uplink signals and downlink signals. The LTE that adopts the TDD system is also referred to as TD-LTE or LTE TDD. The TDD is a technology that enables full-duplex communication in a single frequency band by performing time-division multiplexing on uplink signals and downlink signals. The details of the FD-LTE and the TD-LTE are disclosed in NPL 1.
The base station apparatus may transmit, to the terminal device, a reference signal (referred to as RS) which is a known signal between the base station apparatus and the terminal device. As the reference signal, a plurality of reference signals may be transmitted for various purposes such as demodulation of a signal channel or reporting of a channel state. For example, a cell-specific reference signal is transmitted as a reference signal specific to the cell in all downlink subframes. For example, a UE-specific reference signal is transmitted as a reference signal specific to the terminal device in a resource to which a data signal for the terminal device is mapped. The details of the reference signals are disclosed in NPL 1.
In the 3GPP, the introduction of a small cell has been examined. The small cell is the general term for cells of which a transmit power of the base station apparatus constituting this cell is low and coverage is narrower than that of the cell (macrocell) of the related art. For example, since the small cell is applied in a high frequency band, it is possible to arrange the small cells with high density, and an effect of improving spectral efficiency per area is exhibited. In the examination of the introduction of the small cell, a technology that switches the state of the base station apparatus to a deactivated state has been examined for various purposes such as low power consumption or inter-cell interference reduction. The details thereof are disclosed in NPL 2.